JP2008111948A - Fixing roller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing roller having the releasability of a recording medium, antistatic characteristic and durability with simple constitution. <P>SOLUTION: The fixing roller 10 is constituted by successively covering the outer periphery of a hollow cylindrical core bar 1 with a conductive primer layer 2, a conductive intermediate layer 3 and a non-conductive outermost layer (releasing layer) 4. The intermediate layer 3 is composed by dispersing conductive material 5 in a non-conductive fluororesin layer, and has a rough surface formed with many projecting parts 3a and recessed parts 3b. The outermost layer 4 is formed only of non-conductive fluororesin, and has a smooth surface in order to secure the excellent releasing property of the recording medium. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing roller used in a fixing device for fixing an image on a transfer sheet by heating and pressing in an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic system.

  The configuration of a conventional image forming apparatus is shown in FIG. Reference numeral 100 denotes an image forming apparatus, which shows a digital multi-function peripheral as an example. In the image forming apparatus 100, when performing a copy operation, the image reading unit 102 reads the image forming unit P disposed above the transport belt 101 in the main body of the MFP by the charging, exposure, development, and transfer processes. A predetermined image is formed based on the original image data.

  The image forming portion P is provided with a photosensitive drum 103 that carries a visible image (toner image), and the toner image formed on the photosensitive drum 103 moves adjacent to the image forming portion. The image is transferred onto a sheet (recording medium) 104 carried and conveyed by the conveying belt 101, and after being fixed on the sheet 104 by the fixing device 105, the sheet is discharged from the apparatus main body. An image forming process is performed on the photosensitive drum 103 while rotating the photosensitive drum 103 clockwise in FIG.

  Next, the image forming unit P will be described in detail. Around and around the photosensitive drum 103 rotatably arranged, a charger 106 for charging the photosensitive drum 103, an exposure unit 107 for exposing image information to the photosensitive drum 103, and the photosensitive drum 103 A developing device 108 for forming a toner image and a cleaning unit 109 for removing the developer (toner) remaining on the photosensitive drum 103 are provided.

  First, the surface of the photosensitive drum 103 is uniformly charged by the charger 106, and then light is irradiated by the exposure unit 107 to form an electrostatic latent image corresponding to the image signal on the photosensitive drum 103. The developing device 108 is filled with a predetermined amount of toner by a toner container 110. This toner is supplied onto the photosensitive drum 103 by the developing device 108 and is electrostatically attached, so that a toner image corresponding to the electrostatic latent image formed by exposure from the exposure unit 107 is formed.

  The sheet 104 onto which the toner image is transferred is stored in a sheet storage unit 111 including a plurality of paper feed cassettes 111a, 111b, and 111c for storing paper and a stack bypass (manual feed tray) 111d provided above the sheet cassette. The paper is supplied onto the conveyance belt 101 via the paper feed roller 112 and the registration roller 113 and is conveyed to the position of the photosensitive drum 103. A sheet made of dielectric resin is used for the conveyance belt 101, and a belt in which both ends thereof are overlapped and joined to each other to form an endless shape or a seamless belt is used.

  The conveyor belt 101 is stretched between a downstream drive roller 114 and an upstream driven roller 115. When the conveyor belt 101 starts to rotate counterclockwise in the figure, the sheet 104 is conveyed from the registration roller 113. It is conveyed onto the belt 101. At this time, the image writing signal is turned ON, and an image is formed on the photosensitive drum 103 at a predetermined timing. The toner on the photoconductive drum 103 is transferred at a transfer nip N between the photoconductive drum 103 and a transfer roller 116 to which a predetermined transfer voltage is pressed against the lower portion of the photoconductive drum 103 via the conveying belt 101. The image is transferred onto the sheet 104. The sheet 104 is held on the conveyor belt 101 with an electrostatic adsorption force.

  The sheet 104 on which the toner image has been transferred is separated from the conveyance belt 101 and conveyed to the fixing device 105. In addition, the photosensitive drum 103 after the toner image is transferred is removed by the cleaning unit 109 in preparation for the subsequent formation of a new electrostatic latent image. The sheet 104 conveyed from the conveyance belt 101 to the fixing device 105 is heated and pressed by the fixing roller pair 117 to fix the toner image on the surface of the sheet 104, and a predetermined image is formed. Thereafter, the sheet 104 on which the image is formed passes through the conveying roller pair 118 and 119 and is discharged onto the discharge tray 121 from the discharge roller pair 120.

  In the electrophotographic image forming apparatus, as shown in FIG. 9, a heat source is incorporated in at least one of the fixing roller pair 117 forming a nip to form a fixing roller (heating roller), and the nip portion of this roller pair A heat roller fixing system in which toner is fixed to a sheet by inserting a sheet carrying an unfixed toner image into the sheet is widely used. In such a heat roller fixing method, since non-adhesiveness to toner is strongly required for the fixing roller, a non-conductive fluororesin layer having excellent releasability is formed on the surface of the fixing roller by coating or tube coating. Often done.

  However, since the fixing roller is rubbed by the recording medium and the pressure roller, when the surface of the fixing roller is formed of a non-conductive, that is, insulating, pure fluororesin layer, the fluororesin layer is greatly negative due to frictional charging. There is a problem that electrostatic offset is likely to occur when (−) is charged and the toner has a positive (+) polarity. In addition, the pure fluororesin layer has a difficulty in mechanical strength, and it has been difficult to extend the life of the fixing roller in terms of wear resistance.

  Therefore, a method for improving the electrostatic offset by imparting conductivity to the surface of the fixing roller has been proposed. For example, Patent Document 1 discloses a method in which conductive carbon black is dispersed in a fluororesin layer as a release layer. A method of suppressing frictional charging of the fixing roller is disclosed. However, in the method of Patent Document 1, the smoothness of the surface of the fluororesin layer is lowered by the addition of carbon black, and the releasability of the recording medium is also lowered. In addition, when an insulating or conductive wear-resistant material is added to improve wear resistance, the smoothness and releasability of the surface of the fluororesin layer cannot be avoided.

Further, in Patent Document 2, the surface of a conductive cylindrical cored bar is roughened in a crest-valley shape, and a non-conductive fluororesin layer is coated thereon to thereby form a tip of a peak on the surface of the cored bar. A fixing roller is disclosed in which a conduction path using dielectric breakdown is formed between a portion and a non-conductive fluororesin layer surface to suppress the occurrence of electrostatic offset. However, even in the method of Patent Document 2, the part where the tip of the core metal ridge is exposed from the surface of the non-conductive fluororesin layer has poor releasability, and toner, paper powder, etc. are likely to adhere. There was a problem. Depending on the ratio of the exposed portion of the core metal to the entire roller surface, the volume resistance value of the roller may swing to the low resistance side, so that the transfer current applied to the transfer roller flows into the fixing roller through the recording medium. The fixing roller is charged by current leakage, and there is a possibility that electrostatic offset occurs.
JP 2000-338810 A JP 2004-302183 A

  In view of the above problems, an object of the present invention is to provide a fixing roller having both a releasability, an antistatic property, and durability of a recording medium with a simple configuration.

  In order to achieve the above object, the present invention provides a cylindrical cored bar formed of a conductive material, a conductive primer layer covering the outer peripheral surface of the cored bar, and a conductive core layer covering the primer layer. A fixing roller comprising an intermediate layer composed of a fluororesin layer and an outermost layer composed of a non-conductive fluororesin layer covering the intermediate layer, wherein the outer surface of the intermediate layer is a rough surface having concave and convex portions It was.

  In the fixing roller having the above-described configuration, the shortest distance between the surface of the outermost layer and the tip of the convex portion is 10 μm or less.

In the fixing roller having the above-described configuration, the volume resistivity at an applied voltage of 100 V is 10 ¹⁰ Ω / □ or more, and the volume resistivity at an applied voltage of 500 V is 10 ⁸ Ω / □ or less.

  In the fixing roller having the above-described configuration, the intermediate layer has a surface roughness (Rz) of 10 μm or more and a thickness of the intermediate layer or less. In the present specification, the ten-point average roughness is referred to as surface roughness (Rz).

  According to the present invention, in the fixing roller having the above-described configuration, the outermost layer is formed of at least one selected from PFA, PTFE, and FEP.

  According to the present invention, in the fixing roller having the above-described configuration, the intermediate layer contains at least one selected from PFA, PTFE, and FEP and at least one selected from carbon, graphite, and metal oxide. It is characterized by being.

  In the fixing roller having the above-described configuration, the outermost layer has a surface roughness (Ra) of 0.5 μm or less. In the present specification, the center line average roughness is referred to as surface roughness (Ra).

  According to the first configuration of the present invention, the outermost layer, which is a non-conductive fluororesin layer, exhibits excellent releasability at the initial printing stage and can suppress initial electrostatic offset due to transfer current leakage. After continuous printing, a conductive path is formed by dielectric breakdown between the convex portion of the intermediate layer, which is a conductive fluororesin layer, and the surface of the outermost layer, and the negative charge on the roller surface accumulated by frictional charging is applied to the core metal. Therefore, electrostatic offset due to frictional charging can be suppressed. Furthermore, since the conductive material dispersed in the intermediate layer acts as an abrasion resistant material, the progress of wear of the outermost layer is suppressed, and the releasability after continuous printing is ensured.

  According to the second configuration of the present invention, in the fixing roller having the first configuration, the shortest distance between the surface of the outermost layer and the tip of the convex portion of the intermediate layer is 10 μm or less, so that the outermost layer Electric charge conduction is likely to occur between the surface and the convex portion of the intermediate layer, and the effect of suppressing electrostatic offset can be enhanced.

According to the third configuration of the present invention, in the fixing roller having the first or second configuration, the volume resistivity at an applied voltage of 100 V is 10 ¹⁰ Ω / □ or more, and the volume resistivity at an applied voltage of 500 V. By setting it to 10 ⁸ Ω / □ or less, in the initial image where the applied voltage is as low as 100 V, the roller surface becomes high resistance and reliably prevents the transfer current from flowing from the roller surface to the core metal, and the applied voltage is 500 V. During continuous printing, the roller surface has a low resistance, and the negatively charged surface of the roller that has been frictionally charged can be easily removed to the core.

  According to the fourth configuration of the present invention, in the fixing roller having any one of the first to third configurations, the intermediate layer has a surface roughness (Rz) of 10 μm or more and a thickness of the intermediate layer or less. By doing so, it is possible to improve insulation at the initial stage of printing and to easily cause dielectric breakdown between the outermost layer and the intermediate layer at the end of continuous printing.

  Further, according to the fifth configuration of the present invention, in the fixing roller having any one of the first to fourth configurations, the outermost layer is configured by at least one selected from PFA, PTFE, and FEP. In addition, the outermost layer of the fixing roller excellent in insulation and releasability can be realized at low cost.

  According to the sixth configuration of the present invention, in the fixing roller having any one of the first to fifth configurations, at least one selected from PFA, PTFE, and FEP includes carbon, graphite, and metal oxide. By forming the intermediate layer by containing at least one selected from those, an intermediate layer of the fixing roller having excellent conductivity and wear resistance can be realized at low cost.

  Further, according to the seventh configuration of the present invention, in the fixing roller having any one of the first to sixth configurations, the outermost layer has a surface roughness (Ra) of 0.5 μm or less, thereby further separating. The fixing roller has excellent moldability.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of the fixing roller of the present invention as viewed from the direction of the rotation axis, and FIG. 2 is a partial vertical cross-sectional view of the fixing roller (cross section AA ′ in FIG. 1). As shown in FIG. 1, the fixing roller 10 has a conductive primer layer 2, a conductive intermediate layer 3, and a non-conductive outermost layer (release layer) 4 on the outer peripheral surface of a hollow cylindrical cored bar 1. It is the structure formed sequentially.

  As the material of the core metal 1, a conductive metal material such as aluminum, iron, stainless steel or the like is used. The diameter, length, and thickness of the cored bar 1 are appropriately set according to the size of the fixing device in which the fixing roller is incorporated. Usually, the outer diameter is 15 to 70 mm, the length is 250 to 500 mm, the thickness is 0. The thing of about 3-5 mm is used. The outer peripheral surface of the cored bar 1 is preferably roughened by sandblasting, etching, liquid honing or the like. This is because the adhesion of the primer layer 2 is improved by the primer layer 2 entering the irregularities on the rough surface (anchor effect).

  The primer layer 2 functions as a binder layer that ensures adhesion between the cored bar 1 and the intermediate layer 3. As a material for the primer layer 2, a fluororesin such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), or the like is preferably used. The layer thickness of the primer layer 2 is not particularly limited, but is preferably in the range of 1 μm to 10 μm.

  The intermediate layer 3 is obtained by dispersing the conductive material 5 in a non-conductive fluororesin layer, and the surface is a rough surface on which a large number of convex portions 3a and concave portions 3b are formed. Examples of the non-conductive fluororesin include the above PTFE, PFA, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or a mixture thereof. Examples of the conductive material 5 include carbon, graphite, metal oxides such as titanium oxide, and mixtures thereof. For example, the addition amount when titanium oxide is used as the conductive material 5 is preferably 5% by weight or more from the viewpoint of imparting conductivity, and preferably 15% by weight or less from the viewpoint of workability during production. The layer thickness of the intermediate layer 3 is also related to the surface roughness (Rz) of the intermediate layer 3 described later, but is preferably in the range of 10 μm to 30 μm.

  The outermost layer 4 is formed only from a non-conductive fluororesin, and FEP, PTFE, PFA, or a mixture thereof is used as the material thereof as in the intermediate layer 3. The layer thickness of the outermost layer 4 is preferably in the range of 5 μm to 15 μm. Further, the surface of the outermost layer 4 needs to be a smooth surface in order to ensure good releasability of the recording medium, and is preferably a smooth surface having a surface roughness (Ra) of 0.5 μm or less.

  In the fixing roller 10 of the present invention, since the outermost layer 4 is a non-conductive fluororesin layer, there is no problem with respect to the releasability of the recording medium in the initial state. Further, immediately after the start of use, the outermost layer 4 on the roller surface is not triboelectrically charged and has an insulating property, so that transfer current loss (transfer current leakage) due to transfer current flowing through the recording medium does not occur. . Therefore, image fusion and electrostatic offset do not occur in the initial printing image, and a good image output is performed.

  Further, when continuous printing is performed, the surface of the fixing roller 10 is gradually charged negative (−) due to friction with the recording medium, but when the surface potential reaches a certain level, the convex portion of the intermediate layer 3 Dielectric breakdown occurs between the tip of 3a and the surface of the outermost layer 4, and a charge conduction path is formed to allow current to flow. This action prevents a large negative charge on the surface of the fixing roller 10 and can effectively suppress electrostatic offset.

  At this time, the smaller the shortest distance L between the tip of the convex portion 3a and the surface of the outermost layer 4, the greater the effect of suppressing electrostatic offset. If L exceeds 10 μm, it becomes difficult to form a conduction path due to dielectric breakdown and static The effect of suppressing electric offset is reduced. Therefore, L is preferably 10 μm or less. In addition, in order to improve insulation in the initial stage of printing and to easily generate dielectric breakdown when printing is performed continuously and the surface of the fixing roller is charged, the surface roughness (Rz) of the intermediate layer 3 is set to 10 μm or more. It is preferable to keep it. Thereby, even if the distance between the tip of the convex portion 3a and the surface of the outermost layer 4 is reduced, the thickness of the outermost layer 4 is 10 μm or more in the concave portion 3b, so that insulation in the initial printing is ensured. The upper limit value of the surface roughness (Rz) of the intermediate layer 3 is necessarily equal to or less than the layer thickness of the intermediate layer 3.

As for the electrical characteristics of the fixing roller 10, when the applied voltage is low, that is, in the initial state in actual use, the behavior on the insulation or high resistance side (volume resistance value of 10 ¹⁰ Ω / □ or more) In the case where the roller surface is high, that is, in a state where the roller surface is charged by continuous printing or the like, it is desirable to exhibit a behavior on the low resistance side (10 ⁸ Ω / □ or less in volume resistance). This electrical characteristic will be described in detail in Examples.

  Here, as the number of printed sheets increases, the outermost layer 4 on the roller surface wears. However, in the configuration of the present invention, the tip of the convex portion 3a of the intermediate layer 3 is located near the surface of the outermost layer 4. Thus, the effect of improving the wear resistance is recognized. As shown in FIG. 3, when the surface 4a of the outermost layer 4 is worn from the initial state (broken line in the figure) and reaches the tip of the convex portion 3a, titanium oxide or the like dispersed in the intermediate layer 3 This is because the conductive material 5 acts as an abrasion resistant material and suppresses further wear of the outermost layer 4.

  The fixing roller 10 of the present invention includes, for example, a non-conductive fluororesin layer in which a conductive material 5 such as titanium oxide is dispersed after a primer layer 2 is applied to the outer peripheral surface of a cylindrical core metal 1 by spraying or the like. The intermediate layer 3 is formed by coating. Next, the surface of the intermediate layer 3 is roughened by sandblasting or the like so that the surface roughness (Rz) is 10 μm or more. The outermost layer 4 is formed by covering the intermediate layer 3 with a non-conductive fluororesin layer, and is polished so that the surface roughness (Ra) is a smooth surface of 0.5 μm or less. The

  Examples of the method of covering the intermediate layer 3 and the outermost layer 4 include a method of coating a fluororesin or a method of covering a fluororesin tube. Examples of the method for smoothing the surface of the outermost layer 4 include polishing methods such as centerless polishing, finisher polishing, tape polishing, and a method of pressing a metal roller.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above embodiment, the wear resistance is improved by the conductive material 5 dispersed in the intermediate layer 3. However, in addition to the conductive material 5, for example, a nonconductive or conductive wear resistant material may be added. . Examples of such wear-resistant materials include organic and inorganic powders such as glass, silica, silicon carbide, diamond and corundum, and metal powders such as nickel and iron.

  Using the fixing roller of the present invention shown in FIG. 1 and FIG. 2, the releasability, abrasion resistance, initial printing performance, and electrostatic offset prevention performance during continuous printing were evaluated. As a fixing roller, an aluminum core 1 having an outer diameter of 30 mm and a thickness of 1 mm, a conductive primer layer 2 having a thickness of 8 μm, a thickness of 18 μm of titanium oxide added as a conductive material 5 to PFA, a thickness of 18 μm, and a surface roughness. (Rz) 12 μm of intermediate layer 3 is sequentially formed, and further the non-conductive outermost layer 4 made of only PFA is coated to make the total thickness of the fluororesin layer (primer layer + intermediate layer + outermost layer) 30 μm. The surface of the outermost layer 4 was subjected to centerless polishing so that the surface roughness (Ra) was 0.5 μm or less. That is, the shortest distance between the surface of the outermost layer 4 and the tip of the convex portion 3a of the roughened intermediate layer 3 is 4 μm, and the longest distance between the surface of the outermost layer 4 and the concave portion 3b is 16 μm.

  Further, as shown in FIG. 4, a fixing roller in which a core 1 is coated with a primer layer 2 and an outermost layer 4 in this order is dispersed in Comparative Example 1, and a nonconductive wear-resistant material 6 is dispersed in the outermost layer 4 as shown in FIG. The fixing roller in which the conductive material 5 is dispersed in the outermost layer 4 as shown in Comparative Example 2 and Comparative Example 3 as shown in FIG. Further, as shown in FIG. 7, a fixing roller in which the core 1 is roughened and the surface is coated with the primer layer 2 and the outermost layer 4 to smooth the surface is referred to as Comparative Example 4, and the core 1 is exposed to a large extent. This was designated as Comparative Example 4A, and the one with a small exposure of the core 1 was designated as Comparative Example 4B. In the fixing rollers of Comparative Examples 1 to 4, similarly to the fixing roller of the present invention, an aluminum cored bar having an outer diameter of 30 mm and a wall thickness of 1 mm was used, and the total thickness of the fluororesin layer was set to 30 μm. Further, other processing conditions such as surface processing of the outermost layer 4 were similarly evaluated as conforming to the fixing roller of the present invention.

  As an evaluation method, the fixing device including the fixing roller of the present invention and Comparative Examples 1, 2, 3, 4A and 4B is mounted on a test machine, a test image is printed, the releasability of the initial image, and the transfer current flow. The initial electrostatic offset by 100, the electrostatic offset after 100 sheets were continuously printed, the wear resistance of the roller after 100,000 sheets were printed, and the releasability at the time of wear were visually observed. The results are shown in Table 1. FIG. 8 shows voltage-resistance characteristics when a DC voltage is applied to the cored bar from the surface of the fixing roller of the present invention and Comparative Examples 1 to 4. In FIG. 8, the volume resistance value (Ω / □) is converted to a logarithm (LogΩ).

  As can be seen from Table 1, the fixing roller of the present invention had very good releasability in the initial image, and no initial electrostatic offset due to transfer current leakage occurred. Further, even after 100 sheets were continuously printed, no electrostatic offset was generated due to frictional and electric resistance on the roller surface. This is because the outermost layer 4 which is non-conductive and smooth in the initial stage of printing exhibits good releasability and insulation, and after the continuous printing, the convex portion 3a of the intermediate layer 3 and the surface of the outermost layer 4 This is considered to be because the occurrence of electrostatic offset is suppressed by the dielectric breakdown of the film. Further, even after 100,000 sheets were printed, the wear on the roller surface was suppressed and the releasability was ensured. This is presumably because the conductive material 5 in the intermediate layer 3 acts as a wear resistant material.

  On the other hand, in Comparative Example 1 in which the core metal 1 was simply coated with the primer layer 2 and the non-conductive outermost layer 4, good release and insulation were exhibited at the initial printing stage, but 100 sheets were continuously printed. Later, electrostatic offset was remarkably generated due to the frictional electric resistance of the outermost layer 4. Furthermore, after printing 100,000 sheets, the roller surface was severely worn. Further, in Comparative Example 2 in which the non-conductive wear-resistant material 6 was added to the outermost layer 4, although the wear resistance was improved as compared with Comparative Example 1, the releasability at the initial stage of printing due to the decrease in the smoothness of the outermost layer 4 surface. The electrostatic offset after continuous printing was not suppressed.

  On the other hand, in Comparative Example 3 in which the conductive material 5 was added to the outermost layer 4, the abrasion resistance and the electrostatic offset suppression effect after 100 sheets of continuous printing were improved as compared with Comparative Example 1, but printing was performed in the same manner as Comparative Example 2. The releasability in the initial stage decreased. Further, since the roller surface is slightly lowered in resistance by the conductive material 5, the occurrence of initial electrostatic offset due to transfer current leakage was observed.

  Of Comparative Example 4 in which the core bar 1 is roughened and the tip of the convex portion of the rough surface is exposed on the surface of the outermost layer 4, in Comparative Example 4A in which the surface area of the cored bar exposed part is large, the releasability from the initial printing stage. In addition, the transfer current leakage increased due to the use of a roller conductor, and the initial electrostatic offset was remarkably generated. On the other hand, in Comparative Example 4B in which the surface area of the cored bar exposed portion was small, the release property at the initial stage of printing was improved, but when the outermost layer 4 was worn, the cored bar part was exposed and the release property was lowered. In addition, the occurrence of initial electrostatic offset due to the low resistance of the roller was also observed.

Here, as is apparent from FIG. 8, in the fixing roller of the present invention, the volume resistance value is 10 ¹¹ to 10 ¹² Ω / □ at an applied voltage of 100 V, and the volume resistance value is from 10 ⁶ to 10 ^{7 at} an applied voltage of 500 V. It was Ω / □. That is, in the initial image where the applied voltage is as low as 100 V, the presence of the non-conductive outermost layer 4 makes the roller surface highly resistant to reliably prevent transfer current leakage from the roller surface to the core metal 1. It was confirmed that, during continuous printing at a high voltage of 500 V, the roller surface became low resistance due to dielectric breakdown, and the negatively charged surface of the roller, which was frictionally charged, easily escapes to the cored bar 1.

On the other hand, in Comparative Examples 1 and 2, the volume resistance value is 10 ¹⁰ Ω / □ or more even when the applied voltage is increased to 500 V, and no current flows from the roller surface to the core 1, so the roller surface during continuous printing It is predicted that the triboelectric charge will not be lost. Further, in Comparative Example 4, it was confirmed that the behavior of the volume resistance value when the applied voltage was changed greatly depending on the degree of exposure of the metal core, and in Comparative Example 4A where the degree of exposure was large, the applied voltage was 100V. The volume resistance value was 10 ¹⁰ Ω / □ or less.

  From the above, the fixing roller of the present invention is superior in both release property and wear resistance as compared with the fixing rollers of Comparative Examples 1 to 4, and generates an electrostatic offset over a long period from the start of use. It was confirmed that suppression was possible. It should be noted that the fixing roller of the present invention used in the above embodiment is only an example, and it is known that the same result can be obtained even with a fixing roller manufactured by a combination of other fluororesin or conductive material, for example. .

  The present invention relates to an intermediate layer comprising a cylindrical cored bar made of a conductive material, a conductive primer layer covering the outer peripheral surface of the cored bar, and a conductive fluororesin layer covering the primer layer And an outermost layer made of a non-conductive fluororesin layer that covers the intermediate layer, and the fixing roller has a rough surface having a concave portion and a convex portion on the outer surface of the intermediate layer.

  As a result, it exhibits excellent releasability in the initial stage of printing, can suppress both initial electrostatic offset due to transfer current leakage and electrostatic offset due to frictional charging, and has excellent wear resistance and a long period of time. It is possible to provide a fixing roller in which a predetermined releasability is ensured even after use.

In addition, since the shortest distance between the outermost layer surface and the tip of the convex portion of the intermediate layer is 10 μm or less, electrical conduction between the outermost layer and the intermediate layer is likely to occur, and the effect of suppressing electrostatic offset is enhanced. be able to. Further, since the volume resistivity at an applied voltage of 100 V is 10 ¹⁰ Ω / □ or more and the volume resistivity at an applied voltage of 500 V is 10 ⁸ Ω / □ or less, the roller surface is high in an initial image with a low applied voltage of 100 V. A fixing roller that reliably prevents initial electrostatic offset and effectively prevents electrostatic offset due to frictional charging during continuous printing when the applied voltage is as high as 500V. Can be provided.

  Further, since the surface roughness (Rz) of the intermediate layer is set to 10 μm or more, the fixing roller can ensure insulation at the initial stage of printing and effectively prevent electrostatic offset by dielectric breakdown at the end of continuous printing. Furthermore, since the surface roughness (Ra) of the outermost layer is smoothed to 0.5 μm or less, the fixing roller is excellent in releasability at the initial stage of printing.

These are the schematic cross sections which looked at the fixing roller of this invention from the rotating shaft direction. FIG. 3 is a partial cross-sectional view of the fixing roller of the present invention. These are the fragmentary sectional views which show the state where the fixing roller of this invention was worn. FIG. 4 is a partial cross-sectional view of a fixing roller of Comparative Example 1; These are partial cross-sectional views of the fixing roller of Comparative Example 2. FIG. FIG. 9 is a partial cross-sectional view of a fixing roller of Comparative Example 3. These are partial cross-sectional views of the fixing roller of Comparative Example 4. These are the graphs which show the voltage-resistance characteristic at the time of applying a direct current voltage to a metal core from the roller surface in the fixing roller of this invention and Comparative Examples 1-4. FIG. 1 is a schematic diagram illustrating an overall configuration of a conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core metal 2 Primer layer 3 Intermediate layer 3a Convex part 3b Concave part 4 Outermost layer (release layer)
4a Surface 5 Conductive material 6 Wear resistant material 10 Fixing roller

Claims (7)

  A cylindrical cored bar made of a conductive material, a conductive primer layer covering the outer peripheral surface of the cored bar, an intermediate layer made of a conductive fluororesin layer covering the primer layer, and the intermediate A fixing roller, wherein the outer surface of the intermediate layer is a rough surface having a concave portion and a convex portion.   The fixing roller according to claim 1, wherein a shortest distance between a surface of the outermost layer and a tip of the convex portion is 10 μm or less. 3. The fixing roller according to claim 1, wherein the volume resistivity at an applied voltage of 100 V is 10 ¹⁰ Ω / □ or more and the volume resistivity at an applied voltage of 500 V is 10 ⁸ Ω / □ or less.   The fixing roller according to claim 1, wherein the intermediate layer has a surface roughness (Rz) of 10 μm or more and a thickness of the intermediate layer or less.   The outermost layer is composed of at least one selected from a tetrafluoroethylene-perfluoroalkoxyethylene copolymer, a polytetrafluoroethylene, and a tetrafluoroethylene-hexafluoropropylene copolymer. The fixing roller according to claim 1.   The intermediate layer is made of at least one selected from a tetrafluoroethylene-perfluoroalkoxyethylene copolymer, a polytetrafluoroethylene, and a tetrafluoroethylene-hexafluoropropylene copolymer, from carbon, graphite, and a metal oxide. The fixing roller according to claim 1, wherein the fixing roller contains at least one selected.   The fixing roller according to claim 1, wherein the outermost layer has a surface roughness (Ra) of 0.5 μm or less.

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